Increased demand in the marketplace for methanol production has led to a search for efficient alternatives to conventional gas phase processes. One alternative is a liquid phase methanol process wherein methanol is produced by contacting a synthesis gas comprising hydrogen and carbon oxides with a catalyst in the presence of an inert liquid. Typically, the synthesis gas is bubbled through the catalyst/liquid mixture wherein a portion of the H.sub.2, CO.sub.2 and/or CO is converted to methanol.
In contrast to conventional gas phase processes using packed-bed reactors which are loaded with up to 70 vol % catalyst, slurry concentration for liquid phase processes is typically limited to the range of 20 to 45 wt % or 10 to 30 vol % based on the volume of catalyst per volume of reactor. Consequently, known processes for producing methanol in the liquid phase require larger and more expensive reactors than required in conventional processes in order to produce the same methanol production rate.
Representative of processes for forming methanol in the liquid phase is U.S. Pat. No. 4,031,123 which discloses a process for the production of methanol from a feed gas containing hydrogen and carbon oxides wherein the feed gas is passed into a reaction zone containing methanol-forming catalyst particles which are suspended in a paraffinic and/or cycloparaffinic liquid having from 6 to 30 carbon atoms. The process is conducted at temperatures from 150.degree. to 400.degree. C. and pressures from about 200 to 10,000 psia.
U.S. Pat. No. 4,567,204 discloses a process for preparing methanol from synthesis gas containing hydrogen and carbon monoxide in a liquid-phase reactor wherein a methanol-forming catalyst is entrained in an inert solvent and the entrained catalyst is contacted with the synthesis gas. The active element of suitable methanol-forming catalysts includes copper, zinc, aluminum, magnesium, zinc, chromium, molybdenum, uranium, tungsten, vanadium and rare earths. The amount of catalyst entrained in the inert liquid ranges from about 5 to 40 wt %.
U.S. Pat. No 4,628,066 discloses a process for increasing the capacity of a gas phase synthesis loop for the production of methanol from a synthesis feed gas wherein the feed gas is initially passed through a liquid phase methanol reactor to convert a portion of the feed gas to methanol. The unreacted feed gas is passed to a gas phase synthesis loop for further conversion and recovery of methanol. Suitable catalysts include those listed in Col. 4 of U.S. Pat. No. 4,031,123. Average catalyst particle size may range from 0.00002 to 0.25 inches depending on the reactor bed type (trickle bed, liquid fluidized or slurry) and liquid flow rate used in the process. Reactor pressure is maintained between 200 psia and 1,000 psia. Reaction temperatures typically range from between 150.degree. C. to 400.degree. C. with best performance obtained between 230.degree. C. and 250.degree. C.
Canadian Pat. No. 1,157,053 also discloses a process for producing methanol in the liquid phase wherein methanol is produced by contacting a synthesis gas comprising hydrogen and carbon oxides with a catalyst in the presence of an inert liquid. Suitable catalysts are in the form of particles having a diameter of less than about 125 microns.